1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode wherein the luminous efficiency is improved by enhancing current spreading performance.
2. Description of the Related Art
GaN-based light emitting diodes (LEDs) have considerably changed LED technologies and are currently used in a variety of applications such as full-color LED displays, LED traffic lights and white LEDs. Recently, high-efficiency white LEDs are expected to replace fluorescent lamps. Particularly, the efficiency of the white LEDs has reached a level similar to that of general fluorescent lamps.
A GaN-based LED is generally formed by growing epitaxial layers on a substrate such as sapphire, and comprises an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. An N-electrode is formed on the N-type semiconductor layer, and a P-electrode is formed on the P-type semiconductor layer. The LED is electrically connected to an external power source through the electrodes to thereby be driven. At this time, current flows from the P-electrode into the N-electrode via the semiconductor layers.
Since the P-type semiconductor layer generally has a high specific resistivity, current is not uniformly distributed in the P-type semiconductor layer but concentrated on a portion at which the P-electrode is formed. In addition, the current flows into the N-electrode via the semiconductor layers. Accordingly, the current is concentrated on a portion at which the N-electrode is formed on the N-type semiconductor layer, and there is a problem in that the current concentratedly flows through an edge of the LED. The current concentration leads to reduction of a light emitting area, and therefore, the luminous efficiency is lowered.
Such a problem is very serious in a large-sized LED of about 1 mm2 or more, particularly used for high luminosity. That is, since current is not spread over a central portion of the LED but mostly flows through a corner or edge of the LED, the luminous efficiency is relatively reduced in the large-sized LED.